CN113027785B - Centrifugal compressor stability expanding method for end wall of dual-function coupling profile control diffuser - Google Patents

Centrifugal compressor stability expanding method for end wall of dual-function coupling profile control diffuser Download PDF

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CN113027785B
CN113027785B CN202110378171.8A CN202110378171A CN113027785B CN 113027785 B CN113027785 B CN 113027785B CN 202110378171 A CN202110378171 A CN 202110378171A CN 113027785 B CN113027785 B CN 113027785B
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end wall
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diffuser
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blade
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CN113027785A (en
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崔琴
秦国良
王懿
贾诚
雷健
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Xian Jiaotong University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D17/00—Radial-flow pumps, e.g. centrifugal pumps; Helico-centrifugal pumps
    • F04D17/08—Centrifugal pumps
    • F04D17/10—Centrifugal pumps for compressing or evacuating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/002—Details, component parts, or accessories especially adapted for elastic fluid pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/40—Casings; Connections of working fluid
    • F04D29/42—Casings; Connections of working fluid for radial or helico-centrifugal pumps
    • F04D29/44—Fluid-guiding means, e.g. diffusers
    • F04D29/441—Fluid-guiding means, e.g. diffusers especially adapted for elastic fluid pumps
    • F04D29/444—Bladed diffusers
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
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Abstract

The invention relates to a centrifugal compressor stability expanding method of a dual-function coupling profile control diffuser end wall, which comprises the following steps: firstly, analyzing a flow structure inducing instability under a small-flow working condition by performing geometric modeling and numerical simulation on an original centrifugal compressor with a blade diffuser, finding out the most critical position for inducing the stall precursor of the compressor, and determining the hub wall surface of the blade diffuser at the position where the stall precursor appears as a modeling critical position; and then transforming the conventional plane end wall into a dual-function coupling profile with concave-convex fluctuation characteristics according to a flow rule, flexibly constructing concave-convex end walls in different forms by adjusting three profile control parameters, and enabling the dual-function coupling profile to be in a periodic array in all blade channels of the diffuser by taking the camber line of each blade as a boundary. The invention changes the flow velocity and pressure distribution near the wall surface by changing the geometric shape of the flow channel, effectively inhibits the flow separation of the centrifugal compressor under the working condition of small flow, and delays the occurrence of rotating stall and surge, thereby widening the stable operation range of the centrifugal compressor.

Description

Centrifugal compressor stability expanding method for end wall of dual-function coupling profile control diffuser
Technical Field
The invention belongs to the technical field of centrifugal compressors, and particularly relates to a centrifugal compressor stability expansion method for a dual-function coupling profile regulation diffuser end wall.
Background
The centrifugal compressor has the advantages of small volume, high single-stage pressure ratio, simple structure and the like, and plays a vital role in the industries of metallurgy, petrifaction, natural gas transportation, refrigeration, electric power and the like. With the continuous advance of the modern industrial process, the development of a centrifugal compressor with high load, wide working condition, high efficiency and miniaturization is one of the current important trends, and more severe requirements are provided for the performance of the centrifugal compressor. The research of domestic and foreign scholars on centrifugal compressors shows that the design of a high-load centrifugal compressor can be realized by an advanced design method, but the problems that the stable operation range is obviously narrowed and the peak efficiency is moved to the surge point can be met. Therefore, the narrow stable operation range of the compressor is an important factor for restricting the development of the centrifugal compressor under high load and wide working condition, and particularly, the stable operation of the centrifugal compressor is seriously damaged by the phenomena of rotating stall and surge under the working condition of small flow. Therefore, the method delays the occurrence of rotating stall and surge through an effective technical means, widens the stable operation range of the compressor, has important significance for improving the performance and reliability of the centrifugal compressor, and is one of the key problems to be solved for the safe and stable operation of the compressor.
For centrifugal compressors with a vane diffuser, the strongly non-uniform flow field at the centrifugal impeller exit causes flow turbulence inside the vane diffuser, and stall precursors first occur in the vaneless and semi-vaneless regions of the vane diffuser. Therefore, it is important to suppress flow separation where the vane diffuser induces stall under low flow conditions. Scholars at home and abroad propose a plurality of active and passive stability augmentation technologies aiming at the instability mechanism of the centrifugal compressor. Passive flow control techniques are widely used with simple devices, low cost, no additional energy input, and the like, such as casing handling, tandem cascade diffusers, adjustable vane diffusers, and the like. These methods have some efficacy in widening the stable operating range of the centrifugal compressor, but make the structure of the vane diffuser relatively complicated, increasing the difficulty of design and manufacture. The non-axisymmetric end wall modeling technology can design the axisymmetric end wall into a concave-convex wavy profile end wall according to a flow rule, and the flow direction and strength of the near-end wall are controlled by changing the geometric shape of the flow channel so as to reduce the flow loss. At present, the research and application of the non-axisymmetric end wall modeling technology in the centrifugal compressor are not mature.
Zhou Li has carried out non-axisymmetric end wall numerical optimization research to a certain centrifugal compressor blade diffuser wheel hub side, adopts behind the optimization end wall diffuser, makes the total pressure loss of design point reduce, but the steady operation scope reduces to some extent. The Lang-entering flower adopts a non-axisymmetric end wall modeling structure in the side inlet area of the wedge-shaped blade diffuser hub, so that the flow in the diffuser passage is redistributed to delay the occurrence of surge, and the stable operation range expansion of 11.8 percent is realized. The Hermann adopts an end wall modeling technology in the inlet area of the hub side of the blade diffuser of the centrifugal compressor, changes the flow airflow angle distribution of the front edge of the blade diffuser, and increases the stable operation range by 8%. Researches show that the non-axisymmetric end wall modeling technology has certain efficacy in widening the stable operation range of the centrifugal compressor. However, the method for modeling the non-axisymmetric end wall of the vane diffuser only provides a thought, and a general method for modeling the non-axisymmetric end wall of the centrifugal compressor is not provided, so that the end wall modeling technology is difficult to be integrated into a design system of the centrifugal compressor. Therefore, the proposal of the non-axisymmetric end wall molding method has important significance for promoting the research of the technology in the centrifugal compressor.
Chinese patent specification No. 106089806 of zhou li of northwest industrial university discloses an end wall processing method for reducing separation loss of a diffuser, and a pair of concave-convex structures with equal amplitude are constructed by using a NURBS curved surface. The end wall processing method reduces the total pressure loss of the compressor, and accordingly improves the peak efficiency and the pressure ratio. However, this method can only change the peak size of the non-axisymmetric end wall structure, and cannot change the circumferential direction concave-convex pattern and the change of the peak along the flow direction, resulting in a single concave-convex end wall pattern to be generated, and cannot realize a variety of concave-convex end wall patterns. And the modeling position of the end wall is not selected at the position of a flow destabilization key, so that the aim of reducing the flow loss at a design point is only achieved, and the effect of expanding stability is not realized.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for stabilizing the centrifugal compressor of a diffuser end wall regulated by a double-function coupling profile.
In order to achieve the purpose, the invention adopts the technical scheme that:
the centrifugal compressor stability expanding method of the end wall of the dual-function coupling profile control diffuser comprises the following steps:
firstly, analyzing a flow structure inducing instability under a small-flow working condition by performing geometric modeling and numerical simulation on an original centrifugal compressor with a blade diffuser, finding out the most critical position for inducing the stall precursor of the compressor, and determining the hub wall surface of the blade diffuser at the position where the stall precursor appears as a modeling critical position;
and then transforming the conventional plane end wall into a dual-function coupling profile with concave-convex fluctuation characteristics according to a flow rule, flexibly constructing concave-convex end walls in different forms by adjusting three profile control parameters, and enabling the dual-function coupling profile to be in a periodic array in all blade channels of the diffuser by taking the camber line of each blade as a boundary.
A further development of the invention is that the dual-function coupling profile within a single cycle comprises the following steps:
step 1: boundary definition is carried out on key positions of end wall modeling in an end wall modeling period, the circumferential boundary is a camber line of adjacent blades, and the flow direction boundary is a camber line at the position of relative meridian flow lines of upstream and downstream of the key region of modeling, so that the wall surface of the hub of the single-period diffuser is divided into a modeling region and a non-modeling region;
step 2: in the end wall modeling area provided in the step 1, a plurality of cutting lines are uniformly selected on the three-dimensional curved surface along the circumferential direction, wherein the initial cutting line and the final cutting line are camber lines of adjacent blades, the rest cutting lines are uniformly distributed in the modeling area, control points are uniformly distributed on each cutting line along the flow direction, so that the modeling area is parameterized into a plurality of control points, and one cutting line is arranged at intervals of 2-degree circumferential angles;
and step 3: adding axial disturbance with a circumferential direction and flow direction superposition effect to the discrete control points in the step 2 according to the flow rule, constructing an end wall profile protruding from the pressure surface to the suction surface by adopting a trigonometric function along the circumferential direction, wherein the control curve of the trigonometric function is
Figure BDA0003012091270000041
Wherein theta is0And thetamThe angular coordinates of the starting point and the ending point of the curve along the circumferential direction are determined, lambda is a frequency coefficient, and the pressure surface is generated to the suction surface by adjusting the size of lambdaThe same concave-convex fluctuation type;
and 4, step 4: compiling the trend of the flow direction end face by adopting a Bezier curve, wherein the Bezier control curve is
Figure BDA0003012091270000042
Wherein
Figure BDA0003012091270000043
By adjusting the control point P on the Bezier curveiGenerating curves with different peak values and different peak value flow direction positions;
and 5: generating superposed axial disturbance of each control point by coupling the circumferential control function and the flow direction control function in the steps 3 and 4, wherein the specific expression is delta z (r, theta) ═ A (r) f (theta), and adding the axial disturbance to the axial coordinate of the discrete point, so that the plane end wall of the modeling area is transformed into a dual-function coupling profile with concave-convex fluctuation characteristics;
step 6: and (4) smoothly connecting the molded area and the unmolded area of the blade diffuser with the concave-convex fluctuation characteristics generated in the step (5) to form a new non-axisymmetric hub wall surface of the blade diffuser.
The invention has the further improvement that in the step 1, the circumferential boundary is a camber line of the adjacent blade, and the flow direction boundary is a circular arc line in a molding key area, namely the relative meridian flow line position between the upstream and the downstream of the stall precursor occurrence position.
A further development of the invention consists in that in step 2, a cutting line is arranged in the circumferential direction at circumferential angles of 2 °.
A further development of the invention is that in step 3 the frequency coefficient is adjusted to change the relief pattern of the coupling profile from the suction side to the pressure side.
The further improvement of the invention is that in the step 4, the peak value is 5-15% of the leaf height.
A further development of the invention is that in step 4, the position of the peak in the flow direction varies in the direction of the flow line, not limited to the center of the curve.
The invention is further improved in that a three-dimensional profile is generated by coupling a circumferential trigonometric function and a flow direction Bezier curve, and axial disturbance with a circumferential and flow direction superposition effect is added to the discrete control points.
The invention has the further improvement that the axial disturbance magnitude of a plurality of discrete points in the modeling area can be flexibly regulated and controlled by changing the frequency coefficient, the peak value magnitude and the peak value flow direction position.
The invention has at least the following beneficial technical effects:
the modeling method of the end wall of the dual-function coupling profile control diffuser can flexibly and conveniently construct end walls in different concave-convex forms by adjusting the frequency coefficient, the size of the peak value and the flow direction position of the peak value, perform geometric modeling and numerical simulation on the centrifugal compressor of the concave-convex end wall blade diffuser, determine the optimal control parameter combination of the dual-function coupling profile which enables the performance of the centrifugal compressor to be improved most effectively by comparing with the centrifugal compressor which does not perform diffuser end wall modeling, and analyze the modeling and stability-expanding mechanism of the end wall of the blade diffuser. Compared with the prior art, the invention has the following advantages:
1. by providing the modeling method for regulating and controlling the end wall of the diffuser by the double-function coupling profile, the profile form of the end wall is flexibly and conveniently controlled by fewer control parameters (frequency coefficient, peak value size and peak value flow direction position) of the profile of the end wall.
2. The wall surface of the hub of the blade diffuser at the position where the stall precursor appears is selected as a modeling key position, the flow instability mechanism and the flow control method are organically combined, and end wall modeling is not performed on the hub surface of the whole blade channel from the front edge of the blade to the tail edge of the blade blindly.
3. The invention can change the flow velocity and pressure distribution near the wall surface by changing the geometric shape of the flow channel, effectively inhibit the flow separation of the centrifugal compressor under the working condition of small flow, and delay the occurrence of rotating stall and surge, thereby widening the stable operation range of the centrifugal compressor.
Drawings
Fig. 1 is a parametric representation of the vane diffuser hub-side end wall of the present invention, wherein B1-B8 represent the names of circumferential cut lines, and R1-R9 represent the names of control points disposed on each cut line;
FIG. 2A hub side circumferential control function and a flow direction control function are shown schematically, wherein rpeakIndicates the position of the flow direction of the peak, ApeakIs the peak amplitude, λ is the frequency coefficient;
FIG. 3 is a graph of the end wall effect of the dual function coupling profile modulation of the present invention;
FIG. 4 is a diagram showing evaluation amounts of stability enhancement effects;
fig. 5 is a centrifugal compressor efficiency characteristic curve corresponding to the diffuser end wall model with the best expansion and stabilization effect.
Description of reference numerals:
1. blade diffuser hub, 2, blade pressure side, 3, blade suction side, 4, first blade mean camber line, 5, second blade mean camber line, 6, blade leading edge, 7, blade trailing edge, 8, the biggest sunken position of molding end wall, 9, the biggest protruding position of molding end wall.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Referring to fig. 1 to 3, the method for shaping the end wall of the dual-function coupling profile control diffuser is applied to a high-pressure ratio centrifugal compressor with a diffuser with wedge-shaped blades. An end wall structure based on coupling profile regulation and control of a trigonometric function and a Bezier curve is arranged on the wall surface of a blade diffuser hub 1, the maximum protruding position 9 of the modeling end wall exists near a blade pressure surface 2 as a result of modeling, and the maximum recessed position 8 of the modeling end wall exists near a blade suction surface 3, so that a flat wall surface with the same axial coordinate value is transformed into a non-axisymmetric end wall with concave-convex fluctuation characteristics in a local area, and the stable operation range of the high-pressure ratio centrifugal compressor is widened by changing the pressure and speed distribution near the wall surface.
In order to achieve the above purpose, the specific operation steps of this embodiment are as follows:
the original centrifugal compressor is geometrically modeled, and the internal flow field of the original centrifugal compressor is subjected to numerical simulation and flow field analysis, so that the stall of the compressor under a low-flow working condition is induced by flow separation close to the front edge of a suction surface on the side of a diffuser blade wheel cover, and therefore the key position of end wall modeling is selected on the local hub wall surface of a blade diffuser close to the front edge, and the flow of bladeless and semi-bladeless areas is mainly improved.
The end wall profiles between adjacent blade passages of the wedge-shaped blade diffuser are in periodic array in the circumferential direction, and the end wall processing process of the blade diffuser between the camber lines of the adjacent blades is a modeling period. The specific implementation steps of the end wall modeling regulated by the dual-function coupling profile in a single period are as follows:
step 1: and (3) carrying out boundary definition on the key positions of the end wall modeling, wherein the circumferential boundary of the end wall modeling area is a first blade mean camber line 4 and a second blade mean camber line 5 which are adjacent, and 5% and 30% of arc lines at positions corresponding to meridian flow lines are taken as the flow direction boundary, so that the end wall of the diffuser hub in a single period is divided into a modeling area and a non-modeling area.
Step 2: as shown in fig. 1, the end wall shaping region determined in step 1 is parameterized, and 8 control lines, named B1-B8, are taken along the circumferential direction in the shaping region, wherein B1 and B8 are taken on the adjacent first blade mean camber line 4 and second blade mean camber line 5, and the remaining 6 lines are uniformly distributed in the shaping region. And then uniformly arranging 9 control points on each cutting line to disperse the cutting lines into control points, namely R1-R9, so that the end wall modeling area is dispersed into 72 control points, the number of the control points is determined according to specific conditions, the modeling area is ensured to be uniformly and smoothly connected, in order to ensure that the modeling area is smoothly and smoothly connected with the non-modeling area, 30 control points (shown in figure 1) on the boundary of the end wall modeling area are fixed points, and 42 control points (shown in figure 1) in the modeling area are free points.
And step 3: using trigonometric functions
Figure BDA0003012091270000081
Constructing a concave end wall profile of the pressure side 2 of the blade to the suction side 3 of the blade, where θ0And theta8The circumferential angular coordinates of control points on the B1 curve and the B8 curve respectively, wherein lambda is a frequency coefficient, the end wall is provided with different concave-convex forms in the circumferential direction by giving lambda equal to 1,2 and 3, and the specific expression is that the concave and convex centers of the end wall profile are far away from the suction surface and the pressure surface of the blade along with the increase of the lambda value;
and 4, step 4: using Bezier curves
Figure BDA0003012091270000082
Wherein
Figure BDA0003012091270000083
k is 0, 1, LL, n, n is 9, the trend of the connection flow direction end face is adjusted by adjusting a control point P on a Bezier curveiControlling the peak value A of the concave-convex end surfacepeakAnd the position r of the peak in the flow directionpeakPeak size ApeakThe height of the blade is generally 5% -15%, in this embodiment the height of the blade is 17mm, and the position r of the peak value along the flow directionpeakThe change in peak position in the flow direction can be achieved by changing between control points R3-R7.
And 5: and (3) coupling the trigonometric function in the step (3) with the Bezier curve in the step (4) to obtain axial disturbance after superposition of circumferential effect and flow direction effect of each discrete point, wherein the specific expression is delta z (r, theta) equal to A (r) f (theta), and adding the axial disturbance to the axial coordinate of each discrete point, so that the modeling process of the side end wall of the hub of the blade diffuser regulated by the double-function coupling profile in one period is completed.
Step 6: and (3) smoothly connecting the modeling area and the non-modeling area of the blade diffuser with the concave-convex fluctuation characteristics generated in the step (5) to form a new non-axisymmetric hub wall surface of the blade diffuser, wherein the hub wall surface of the blade diffuser is provided with a maximum protruding position 9 of the modeling end wall on the pressure side and a maximum recessed position 8 of the modeling end wall on the suction side, as shown in fig. 3.
In this embodiment, the frequency coefficient λ is adjusted to 1,2,3 and the peak size apeakThe method is characterized in that 18 concave-convex end wall structures are constructed at positions of peak values along the flow direction at R3 and R5 for 5%, 10% and 15% of blade heights, centrifugal compressors with different diffuser end wall forms are respectively modeled and numerically simulated, the influences of different diffuser end wall forms on the stable operation condition range and efficiency of the compressor are compared, and the optimal control parameter combination of the coupling profile for realizing the efficient stability expansion of the centrifugal compressor is determined.
The bifunction coupling profile surface optimal control parameter combination is evaluated according to the following evaluation quantity of stability expansion effect, and the schematic diagram of the evaluation quantity is shown in FIG. 4:
stable operating range SR ═ mc-ms
Stall margin improvement:
Figure BDA0003012091270000091
clogging margin improvement amount:
Figure BDA0003012091270000092
stable operation range improvement amount:
Figure BDA0003012091270000093
design point efficiency change:
Figure BDA0003012091270000094
in the formula, Δ SM, Δ CM, Δ SR, m, η respectively represent a stall margin improvement amount, a blockage margin improvement amount, a stable operation range improvement amount, a mass flow rate, and efficiency, subscripts CEW, Baseline respectively represent a compressor after end wall modeling, an original compressor without end wall modification, and subscripts des, c, s respectively represent that the compressor operates at a design point, a near blockage point, and a near surge point.
And under the design rotating speed, carrying out numerical simulation on the centrifugal compressors after the 18 kinds of end wall processing, quantitatively calculating the stability expansion effect evaluation quantity of the centrifugal compressors corresponding to different end wall models, preferentially considering the improvement quantity of the stable operation range, and referring to the efficiency change of a design point when the improvement quantity is the same. The numerical simulation results show that the optimal control parameter combination of the coupling profiles is that the frequency coefficient is 1, the peak value is 10% of the blade height, and the peak value position is at the R3 flow direction position. Fig. 5 shows an efficiency curve of the centrifugal compressor corresponding to the non-axisymmetric end-wall diffuser determined by the optimal control parameter combination, so as to show the end-wall modeling stability-expanding effect, the stall margin of the compressor is increased by 21.7%, the blockage margin is reduced by 3.91%, the overall stable operation range is increased by 17.91%, and the efficiency of the design point is reduced by 0.13%. The compressor does not operate near a blockage point with extremely low efficiency in the actual operation process, but operates in a high-efficiency area near a design point, and the improvement of the stall margin has important significance on the high-efficiency safe and stable operation of the compressor, so that the method for regulating and controlling the end wall modeling of the vane diffuser through the dual-function coupling profile has obvious effect on realizing the high-efficiency stability expansion of the centrifugal compressor.
Through analysis of the internal flow field of the centrifugal compressor, the local end wall of the diffuser hub side changes the flow distribution close to the wall surface at the stall point, indirectly changes the flow distribution at the wheel cover side, delays the flow separation at the front edge of the suction surface at the diffuser wheel cover side, and delays the occurrence of stall, so that the stable operation range of the centrifugal compressor under the low-flow working condition is widened, and the more the peak flow direction position of the coupling profile is close to the leading edge 6 of the blade, the more obvious the improvement effect on the flow of a stall precursor region is exerted. However, the end wall shape ensures the invariance of the section area of the end wall of the diffuser along the circumferential direction, but the throat area is changed, and the peak flow direction position of the coupling profile is close to the leading edge 6 of the blade, so that the throat area is reduced, and the blocking margin is slightly reduced under the working condition of large flow.
Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims (8)

1. The method for stabilizing the expansion of the centrifugal compressor with the end wall of the dual-function coupling profile control diffuser is characterized by comprising the following steps of:
firstly, analyzing a flow structure inducing instability under a small-flow working condition by performing geometric modeling and numerical simulation on an original centrifugal compressor with a blade diffuser, finding out the most critical position for inducing the stall precursor of the compressor, and determining the hub wall surface of the blade diffuser at the position where the stall precursor appears as a modeling critical position;
then, transforming the conventional plane end wall into a dual-function coupling profile with concave-convex fluctuation characteristics according to a flow rule, flexibly constructing concave-convex end walls in different forms by adjusting three profile control parameters, wherein the dual-function coupling profile is in a periodic array in all blade channels of the diffuser by taking a blade mean camber line as a boundary;
the dual function coupling profile modeling in a single cycle comprises the following steps:
step 1: boundary definition is carried out on key positions of end wall modeling in an end wall modeling period, the circumferential boundary is a camber line of adjacent blades, and the flow direction boundary is a camber line at the position of relative meridian flow lines of upstream and downstream of the key region of modeling, so that the wall surface of the hub of the single-period diffuser is divided into a modeling region and a non-modeling region;
step 2: in the end wall modeling area provided in the step 1, a plurality of cutting lines are uniformly selected on the three-dimensional curved surface along the circumferential direction, wherein the initial cutting line and the final cutting line are camber lines of adjacent blades, the rest cutting lines are uniformly distributed in the modeling area, control points are uniformly distributed on each cutting line along the flow direction, so that the modeling area is parameterized into a plurality of control points, and one cutting line is arranged at intervals of 2-degree circumferential angles;
and step 3: adding axial disturbance with a circumferential direction and flow direction superposition effect to the discrete control points in the step 2 according to the flow rule, constructing an end wall profile protruding from the pressure surface to the suction surface by adopting a trigonometric function along the circumferential direction, wherein the control curve of the trigonometric function is
Figure FDA0003378475290000011
Wherein theta is0And thetamThe method comprises the steps that angular coordinates of a starting point and an ending point of a curve along the circumferential direction are adopted, lambda is a frequency coefficient, and different concave-convex fluctuation patterns from a pressure surface to a suction surface are generated by adjusting the lambda;
and 4, step 4: compiling the trend of the flow direction end face by adopting a Bezier curve, wherein the Bezier control curve is
Figure FDA0003378475290000021
Wherein
Figure FDA0003378475290000022
By adjusting the control point P on the Bezier curveiGenerating curves with different peak values and different peak value flow direction positions;
and 5: generating superposed axial disturbance of each control point by coupling the circumferential control function and the flow direction control function in the steps 3 and 4, wherein the specific expression is delta z (r, theta) ═ A (r) f (theta), and adding the axial disturbance to the axial coordinate of the discrete point, so that the plane end wall of the modeling area is transformed into a dual-function coupling profile with concave-convex fluctuation characteristics;
step 6: and (4) smoothly connecting the molded area and the unmolded area of the blade diffuser with the concave-convex fluctuation characteristics generated in the step (5) to form a new non-axisymmetric hub wall surface of the blade diffuser.
2. The method for stabilizing the centrifugal compressor with the dual-function coupling type surface-controlled diffuser end wall according to claim 1, wherein in the step 1, the circumferential boundary is an arc line in the middle of the adjacent blade, and the flow boundary is an arc line in a relative meridian flow line position between the upstream and the downstream of a critical shaping region, namely a stall precursor occurrence position.
3. The method of claim 1, wherein in step 2, a cut line is placed at every 2 ° circumferential angle in the circumferential direction.
4. The method of claim 1, wherein in step 3, adjusting the frequency coefficient changes the concave-convex pattern of the coupling profile from the suction surface to the pressure surface.
5. The method for stabilizing the centrifugal compressor with the dual-function coupling profile control diffuser end wall according to claim 1, wherein in the step 4, the peak value is 5% -15% of the blade height.
6. The method of claim 1, wherein in step 4, the position of the peak along the flow direction changes along the flow line direction and is not limited to the center of the curve.
7. The method for stabilizing the centrifugal compressor with the dual-function coupling profile control diffuser end wall according to claim 1, wherein the three-dimensional profile is generated by coupling a circumferential trigonometric function and a flow direction Bezier curve, and axial disturbance with a circumferential and flow direction superposition effect is added to discrete control points.
8. The method of claim 1, wherein the axial disturbance at discrete points in the modeling area can be flexibly controlled by changing the frequency coefficient, the peak magnitude and the peak flow direction position.
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